Treatment of a wrong body part due to incorrect setup is among leading types of errors in radiotherapy. Safe delivery of a highly conformal dose distribution to a well-defined target volume in radiotherapy is becoming more complicated due to use of advanced treatment techniques such as intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT). Radiotherapy is a complicated multi-step, multi-person process and errors can occur at any point. One cause for radiotherapy errors is geometric miss caused by incorrect patient setup. Geometric miss is typically defined as treatment of incorrect body parts with more than 10 mm spatial discrepancy. Geometric miss can result in significant under-dose to the target which can cause tumor recurrence, and over-dose to healthy tissue with severe normal-tissue complications. In hypo-fractionated radiotherapy such as stereotactic body radiotherapy (SBRT), it may result in even more severe morbidity than traditional radiotherapy.
A challenge in patient setup is to accurately localize a patient, in each treatment session, to a same planned treatment position. The past decade has seen rapid expansion in technological tools and processes to facilitate accurate patient localization. Examples include patient immobilization devices with couch indexing ability and image-guided radiotherapy (IGRT). Indexed patient immobilization devices not only ensure repeatable patient fixation, but also reduce patient setup errors by providing initial approximate target localization. X-ray based image-guided technologies, such as cone beam computed tomography (CBCT), enable the visualization of internal anatomy with sufficient soft tissue contrast. Such technologies allow corrections for misalignment or interfraction motion through registration with reference CT images. Non-radiographic image-guided technology systems such as AlignRT® (Vision RT Ltd., London, UK), SonArray® (Varian Medical Systems Inc., Palo Alto, Calif.), and ExacTrac® (BrainLab AG, Heimstetten, Germany) have also been developed for the purpose of patient setup guidance as well as continuous monitoring throughout treatment. These systems have the potential to eliminate patient setup errors and significantly reduce setup uncertainty.
However, employment of these advanced technological equipment and tools does not guarantee that radiotherapy is immune to setup errors. Patient setup is a process that cannot be automated, and, therefore, is subject to human errors. There are several contributing factors. First, sufficient formal training is not always provided to personnel who operate the devices and interpret the results. Incorrect interpretation leads to incorrect adjustment of treatment position, and, therefore setup errors. For example, a great risk in treating thoracic spine is the treatment of the wrong vertebral body. Due to similarities in bony structure in this region, incorrect alignment could occur as a result of misregistration using either orthogonal imaging or CBCT. Second, as complexity of tools increases, complexity of control over the tools and workload for therapists increases significantly as well, as evidenced by the increasing number of computer monitors, or displays, in a control room. Therapists could lose attention to correctness of treatment delivery when streamlined workflow and standardized control is lacking. Third, while most IGRT devices have great geometric precision, they have limitations which could disadvantageously impact their ability to ensure patient safety. For example, widely used radiographic systems, such as CBCT, do not track patient position change, and thus only represent the position of a patient at the time of image acquisition. After CBCT imaging, a treatment couch could be accidently moved for some reason (e.g., clearance check), and not moved back to an intended treatment position. In addition, CBCT cannot be performed for non-coplanar setups, meaning that imaging position would differ from treatment position. For this reason, therapists on machines equipped with multiple IGRT devices often find themselves switching between devices from one patient to another, depending on a treatment site of each patient. As another example, non-radiographic image-guided technology systems, such as ExacTrac® and AlignRT®, are usually not general-purpose systems and are only applicable to limited disease sites. Fourth, immediate and independent position verification is not always available to a therapist to show that the patient has been positioned exactly as planned, especially when the above-mentioned limitations of the employed IGRT systems are encountered.
Commercially available non-radiographic tracking systems such as ExacTrac®, frameless SonArray®, and AlignRT® have long been used for patient setup and monitoring, due to their high-precision and continuous tracking ability. However, they all have limitations compared to the method and apparatus in accordance with the invention when trying to use them on a large scale as on a general-purpose patient setup system. Designed to monitor patient motion (both translation and rotation) during treatment, ExacTrac® requires at least four (4) infra-red reflective markers to be affixed on a patient in each treatment session, which not only introduces significant workload to a therapist but also may act as a source of error. The frameless SonArray® system, which connects infra-red reflective markers in a fixed pattern to a patient through a bite block, is only employed in the treatment of brain targets. Similarly, 3D surface imaging-based AlignRT® is not for general-purpose use, and is predominantly used only in the treatment of brain, head and neck, or breast patients. Most importantly, each of these known systems lacks a streamlined workflow which may discourage their large-scale use in a busy clinic.
One known method uses one fiducial marker to improve spine image registration robustness. In such known method, a nearly correct transformation can be obtained by aligning the fiducial marker, which significantly improves registration successful rate. However, this known method disadvantageously requires a surgical implantation procedure.